In the known art, there is, for example, a drive system for an induction motor for a railroad vehicle as described in Patent Literature 1 below. It is mentioned in Patent Literature 1 that the drive system includes a plurality of power supply sources including power supply devices that generate direct-current power and power storage devices (storage devices) connected in parallel to the outputs of the power supply devices so as to supply and accumulate direct-current power. The sets of power supply sources are connected, via an open/close-controllable switch, to an inverter device that receives individual supplies of electric power from direct-current output units, and when the power supply source electrically set to an open state by the switch is connected to the power supply source on a connection partner side, the drive system monitors the direct-current output voltage of the power supply source in the open state and the direct-current output voltage of the power supply source on the connection partner side, and it connects the power supply source in the open state when the voltage difference between both the direct-current output voltages is equal to or lower than a predetermined differential voltage.